The invention relate generally to the field of refrigeration systems and, more specifically, to the charging or recharging of such systems with refrigerant and lubricant, particularly automotive air-conditioning systems.
With the increased popularity of air-conditioning systems in vehicles, the necessity for charging or re-charging such systems has become a common function of automotive service stations and garages. To this end, charging stations or service units have been developed over time in an effort to reduce the manhours required for the charging sequence and to improve the reliability and accuracy of the charging sequence. The objective has been to divorce the procedure from the requirement for skilled experts and permit its use by general automotive mechanics, and to free the serviceman from a routine, time-consuming task for much more productive effort.
Accordingly, in the early days of the charging art, elaborate manuals were prepared for the re-charging procedure. As the art developed, attempts have been made to effect constant-flow metering of the charge in association with timers, as well as the provision of visual forms of indicators denoting attainment of a desired condition in the re-charging cycle. This has been accompanied by the development of the aforesaid charging stations in the form of compact, mobile units which contain and dispense lubricant and refrigerant.
The progress of the art over the past 25 years is exemplified in Shoemaker, U.S. Pat. No. 2,499,170; White, U.S. Pat. No. 3,076,319; Wagner, U.S. Pat. No. 3,785,163; Gemender et al, U.S. Pat. No. 3,813,893; and White, U.S. Pat. No. 3,873,289.
Shoemaker U.S. Pat. No. 2,499,270, supplies a predetermined weight of oil and refrigerant to a reservoir for injection into the refrigeration system after evacuation. Wagner U.S. Pat. No. 3,785,163, uses a change of state, from liquid to saturated vapor, for the refrigerant to provide visual indication when an optimum charge has been attained. Gemender et al, U.S. Pat. No. 3,813,893, use a thermostatically controlled valve and a restricted rate of refrigerant flow to permit control of the charge.
White, U.S. Pat. No. 3,076,319, automates the charging sequence by utilizing pressure-responsive elements and a stepper switch. White, U.S. Pat. No. 3,873,289, controls refrigerant flow rate by pressure drop through a restricted orifice and uses timers for sequencing.
It will be noted that the later patentees have found serious disadvantages in the introduction of a pre-weighed quantity of refrigerant and oil into the air-conditioner system, as disclosed by Shoemaker. Therefore, the later patentees have developed other systems of timed injection or pressure-responsive control which do not relate directly to the weight of refrigerant or of oil, despite the fact that weight is the most desirable measure, as it is substantially free of variations resulting from temperature or pressure changes and is consistent with design criteria and specifications.
The present invention avoids the disadvantages of the Shoemaker disclosure by dealing with weight differentials of large reservoirs rather than dealing with the weight of a discrete charge itself. The present invention apparatus avoids the disadvantages and inaccuracies of the later systems, which are not directly related to weight of charge, by directly using weight as the ultimate measure of the desired charge.